A paint bake oven typically includes an oven enclosure into which coated articles are received, typically on a conveyor, a heating system to provide heat for drying or curing the coating and an exhaust system to ventilate fumes and smoke from the oven enclosure. The heating system provides thermal energy to the oven and transfers that thermal energy to the coated object or article. There are two types of heating systems presently in wide use for paint bake ovens of this type, namely convection and radiation. Occasionally, a combination of convection and radiant ovens are used.
A convection heating system transfers heat to the coated object or article by blowing heated convection air onto the coated article, transferring convection heat energy to the coated article. The volumetric flow rate, temperature and velocity of the convection air are controlled to provide the desired rate of heat gain in the coated object. A convection heating system includes a fan or blower for moving the convection air and a heat source for heating the convection air. Filtration is often provided in the convection heating system to remove dirt particles from the convection air before it is blown onto the coated object.
A radiant heating system transfers heat to the coated article by positioning a hot radiator or radiating wall or duct adjacent the coated object. Electromagnetic radiation, primarily in the form of infrared radiation, is exchanged between the radiator and the object. The radiator size, distance from the object and temperature of the radiator are controlled to provide desired rate of heat gain to the coated object. The radiator is typically a metal wall or panel that is heated by circulating hot air into a space behind the radiator from typically a passage or chamber within the radiator. A radiant heating system, similar to a direct fired convection heating system, heats and circulates the hot air inside a passage or chamber within the radiator. Typically, a radiant heating system will include some convection heating directed at specific heavy metal areas. For automotive bodies, for example, this convection heat is directed at the door sill area. The door sill area is typically made from multiple layers of thicker material, such as steel, and the radiant heating alone is not sufficient to properly heat this area. The convection air may also be directed from a fresh supply for the radiant portion of the oven.
In either type of heating system, a heater box is typically used to house the filters and a heat exchanger (if required) to provide a place to connect the recirculation fan and burner. The heater box also provides a closed space to allow mixing of the burner heat with the recirculating air. The heater box is connected to the oven enclosure by ductwork for conveying air between the oven and the heater box. The heater box or boxes must be insulated to reduce heat loss and reduce the burn hazard to personnel in the area. Further, regardless of the type of heating system used, fresh air make-up is required for the oven. The purpose of fresh air make-up is to replace the air removed from the oven enclosure by the oven exhaust system used to remove combustible gases. With a conventional heating system, the fresh hair make-up is provided by drawing some pressure into the convection heater box. With a radiant heating system, fresh air is provided by a separate fresh air heating system. The fresh air heating system is essentially a convection system with capacity sufficient for the fresh air needs of the oven. It is also possible to allow fresh air to leak into the oven without heating; but this is generally not done because (1) it can lead to condensation problems when the cold air mixes with the hot air inside the oven, and (2) may carry dirt into the oven which would contaminate the coated article.